Biomedical subjects
Publications and source records attributed to E Marder.
A glutamate-activated inhibitory response on a 'crustacean neuromuscular preparation that receives cholinergic excitatory innervation is described. Glutamate produced a dose-dependent conductance increase to C1-ions. The response was mimicked by ibotenic acid, but not by quisqualic acid, and was blocked by picrotoxin.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A pharmacological analysis was made of the depolarizing acetylcholine (ACh) response found on the gastric mill I muscles of the crabs Cancer pagurus, Cancer irroratus and Cancer borealis. Acetylcholine, carbamylcholine, trimethylammonium, nicotine, and dimethyl-4-phenyl-piperazinium were effective in producing contractures and depolarizations in these muscles. No response to decamethonium, suberyldicholine, acetyl-beta-methylcholine, carbamyl-beta-methylcholine, pilocarpine and oxotremorine could be detected. High concentrations of muscarinic agonists (10(-4) to 10(-3) M) potentiated and prolonged the ACh iontophoretic response. When the acetylcholinesterase activity was inhibited with neostigmine, or when the response was elicited with carbamylcholine, muscarinic agonists partially inhibited the response. ACh responses were most effectively blocked by vertebrate nicotinic ganglionic antagonists, including dihydro-beta-erythroidine, pempidine, and mecamylamine. alpha-Bungarotoxin was without effect on the ACh response.
1. A study was performed of the L-glutamate, gamma-aminobutyric acid (GABA), and acetylcholine (ACh) responses of cells in the stomatogastric ganglion of the crab, Cancer pagurus. 2. Ionophoretic or pressure application of L-glutamate revealed three classes of responses: a K+-dependent inhibition which reversed at 15-20 mV more negative than the resting potential; a Cl- dependent inhibitory response which was at equilibrium at the resting potential; and a depolarizing response. 3. Ionophoretic or pressure applications of GABA likewise produced three kinds of responses: an increase in K+ conductance, an increase in Cl- conductance, and a depolarizing response. 4. Picrotoxin (10(-6)-10(-5) M) was effective in blocking both the glutamate inhibitory responses. 10(-4) M-picrotoxin, which was necessary to produce a 50% block of the GABA-K+-dependent response, had no effect on the GABA-Cl- response. 5. beta-Guanidinopropionic acid (beta-GP) was found to be an agonist for the GABA-K+ response, but was ineffective in mimicking or blocking the GABA-Cl- response. 6. ACh applications produced large depolarizing responses with a pharmacological profile similar to that of the nicotinic ganglionic response in vertebrates. 7. The muscarinic agonist, acetyl-beta-methyl choline (MeCh), produced depolarizations which decreased in amplitude as the membrane was hyperpolarized from -40 to -100 mV. Pilocarpine and oxotremorine produced changes in the endogenous activity of ganglionic neurones. 8. Implications of these results for the identification of synaptic transmitters in the somatogastric ganglion are discussed.
1. A study of the neurotransmitters used by each of the eleven types of excitatory motor neurones (identified according to the muscle innervated) of the lobster stomatogastric ganglion was undertaken. 2. The dorsal dilator muscle is innervated by the two motor neurones designated 'PD'. Bath and iontophoretic applications of acetylcholine (ACh) produce contractures and depolarizations respectively in the dorsal dilator muscle. 3. Pharmacological experiments support the cholinergic nature of the excitatory junctional potentials (e.j.p.s) recorded in the dorsal dilator muscle when the PD motor nerve is stimulated. 4. The apparent reversal potentials for the e.j.p.s and the iontophoretic ACh response in the dorsal dilator muscle are the same. 5. On the basis of choline acetyltransferase assays on identified stomatogastric ganglion motor neurone somata and tension measurements on the muscles innervated by each type of stomatogastric ganglion motor neurone, a transmitter candidate was established for each type of motor neurone. Motor neurones named VD, LPG, GM, MG, LG, and DG are putatively cholinergic. L-Glutamate is a transmitter candidate for the motor neurones called LP, PY, IC, and AM. 6. Potential correlations between the distribution of putatively cholinergic and glutaminergic motor neurones and the electrical coupling among the stomatogastric ganglion motor neurones are discussed.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
In a study of the possible mechanisms of the clinical side effects of metrizamide, it was applied to several in vitro model preparations. It was shown that, although high metrizamide concentrations are without noticeable effect on many basic neuronal functions, metrizamide does interfere with cholinergic mechanisms. At concentrations equivalent to, or significantly lower than, those probably achieved during clinical procedures, metrizamide is both an inhibitor of the enzyme acetylcholinesterase and an antagonist of cholinergic transmission. These data suggest the possibility that some of the side effects resulting from clinical procedures employing metrizamide may be explained by its actions on cholinergic synapses.